1. Field of the Invention
This invention relates to the continuous operation of electrochemical cells. More particularly it relates to continuous operation of electrochemical cells which produce a particulate product substantially insoluble in the electrolyte in which it is formed. The process is especially useful for the continuous operation of an electrochemical cell, when a slurry is formed in only one side of the cell. The process of this invention is especially adaptable to the continuous electrochemical preparation of metal alkoxides in the anodic compartment of a separated cell.
The process of this invention is particularly useful for preparing antimony glyoxide. When an electrochemical cell is used for that purpose, the anode is a sacrificial one made from antimony. Ethylene glycol is the reactive medium for the conducting electrolyte. If an effective separator is employed, the antimony cations are confined to the anolyte, glyoxide anions migrate from the catholyte to the anolyte, and a slurry of antimony glyoxide product forms in the anode compartment.
When the product of an electrochemical synthesis is insoluble in the electrolyte, it is difficult to operate the cell continuously. Particulate product coats the electrode and the separator thus raising electrical resistance and lowering current density. The process must be halted periodically to clean the electrodes, separators, cell, agitators, and exit valves. If an attempt is made to circulate the electrolyte continuously, pumps, flow meters, valves, and pipes or tubes get clogged with precipitate. In such a situation cleaning is laborious and the yield of product falls because of waste. If aliquots are removed periodically to isolate the insoluble product, they must be filtered and the filter cake washed free of electrolyte. As a result of such filtration either electrolyte is continuously wasted or becomes diluted with unwanted wash liquid. Intermittent filtration increases labor, raises chemical losses, and increases wear by tolerating medium to high levels of dispersed solids throughout the equipment.
The process of this invention solves many of the problems commonly associated with running an electrochemical process continuously, when the product is insoluble in the electrolyte. Metal alkoxides in general and antimony glyoxide specifically are examples of such insoluble products. Surprisingly, yield is increased, current density is maintained, and the cell is kept clean during continuous operation.
2. Description of the Prior Art
Applicants know of no prior art directly relating to the process of this invention.
A process for the production of tetraethyl lead is described in U.S. Pat. No. 3,069,334 granted to Ziegler et al on Dec. 18, 1962. The process of Ziegler et al employs a cellulosic or glass fiber diaphragm to separate an anolyte and a catholyte of different chemical composition relating to the production of an intermediate, aluminum trimethyl. Both anolyte and catholyte liquids are continuously circulated to and from separate storage vessels. In the catholyte circuit aluminum, an intermediate by-product/component of the intermediate aluminum triethyl, is separated from a complex aluminum triethyl-sodium fluoride by a settling tower. In another embodiment disclosed by Ziegler et al two immiscible liquid intermediates in the anolyte circuit are continuously passed through a counter-current extraction centrifuge after cooling in order to remove the heavier liquid, molten lead.
3. Objects of the Invention
The principal object of the instant invention is to provide a process to operate continuously electrochemical cells which produce an insoluble, particulate product. Another object of the invention is to provide a process for producing metal alkoxides continuously, e.g. antimony ethyleneglyoxide. A further object of the invention is to provide a method to remove insoluble product from an electrochemical process, which generates a slurry in the electrolyte. Still a further object of the invention is to keep electrochemical cells clean and electrodes and separators free of particulate deposits, so that electrical resistance is minimized. Another object of the invention is to maximize chemical yield from a continuously run electrochemical cell producing particulate products, especially metal alkoxides. Yet another object of the process of this invention is to decrease the labor in producing metal alkoxides continuously. Other objects will be apparent to those skilled in the art from the description and examples which follow, as well as by inspection of the Figure.